This invention relates to a cab for construction machines, which can be suitably applied, for example, to hydraulic excavators, hydraulic cranes and the like.
Generally, construction machines such as hydraulic excavators, for example, are largely constituted by a lower structure, an upper structure which is rotatably mounted on the lower structure, and a working mechanism which is provided on a front portion of the upper structure for lifting loads up and down. A cab is provided on a revolving frame of the upper structure as an operating room to be occupied by an operator at the control of the machine.
The cabs of hydraulic excavators of this sort are usually formed in a box-like shape, from a standpoint of protecting operators. As for an example of such cabs for hydraulic excavators, there has been known a box-like cab construction, including mount bases located at four corners and each provided with an upward fitting joint projection, base link frames connecting the four mount bases in transverse and longitudinal directions, right and left front pillars erected on right front and left front mount bases, right and left rear pillars erected on right rear and left rear mount bases, right and left roof pillars connecting upper end portions of the front and rear pillars, a front tie frame connecting upper end portions of right and left front pillars, and a rear tie frame connecting upper end portions of right and left rear pillars (e.g., as disclosed in Japanese Laid-Open Patent Publication No. 2000-198469).
In an assembling stage, the prior art cab is built up firstly by fitting lower ends of left and right front pillars on the fitting joint projection of the mount bases, and is welding fitted lower ends of the respective pillars to the mount bases to erect them thereon.
More specifically, in the case of the above-mentioned prior art construction machine cab, front and rear pillars are erected on mount bases by fitting lower ends of the respective pillars on joint projections which are provided on the side of the mount bases and forming a weld around the circumference of distal end portions which are abutted on the respective mount bases.
However, when welding a lower end of a pillar which is abutted against a mount base, a weld can be formed only around the circumference of distal or root end which is abutted against the mount base. Therefore, due to a limit on the welding distance, it has been difficult to enhance the strength of the weld joint portions of a pillar and a mount base. In addition, because of concentration of stress at a distal end portion or root portion of an erected pillar, the weld which is formed only around the circumference of abutted distal end portions of a pillar is susceptible to damages, which can detrimentally impair the reliability of the machine.
In view of the above-discussed problem with the prior art, it is an object of the present invention to provide a cab for a construction machine, which is so arranged to facilitate positioning of left and right front pillars as well as left and right rear pillars on the respective mount bases and at the same time to increase the strength of their joint portions.
According to the present invention, there is provided a cab for construction machines, including mount bases located at four corners and each provided with an upward fitting joint projection; base link frames arranged to connect the mount bases in transverse and longitudinal directions of a machine; left and right front pillars erected on left and right front mount bases; left and right rear pillars erected on left and right rear mount bases; left and right roof pillars arranged to longitudinally connect upper end portions of the front and rear pillars; a front tie frame arranged to transversely connect upper end portions of the left and right front pillars; and a rear tie frame arranged to transversely connect upper end portions of the left and right rear pillars.
In order to solve the above-discussed problems with the prior art, the cab according to the present invention as defined in claim 1 comprises: a notched portion provided in a lower end portion of each one of the front and rear pillars for fitting engagement with the fitting joint projection of the mount base; a lower end portion of each one of the front and rear pillars being fitted on the fitting joint projection of the mount base and securely fixed to the latter by a weld formed along and between marginal edge portions around the notched portion and the fitting joint projection.
With the arrangements just described, the respective front and rear pillars can be readily and correctly set in position on the respective mount bases by engagement with the fitting joint projections. In addition, in welding lower end portions of the front and rear pillars to the respective mount bases, a weld can be formed along and between marginal edge portions around the notched portions and the fitting joint projections in such a way as to prolong the welding distance and away from a distal or root end portion of the pillar where concentration of stress occurs. Thus, the above arrangements make it possible to increase the strength of welded joint portions.
According to a preferred form of the present invention, the notched portion in each one of the front and rear pillars is in the form of an opening of an inverted U-shape corresponding to profile of the fitting joint projection on the side of the mount base.
With the arrangements just described, a pillar which is set in position on a mount base, with its notched portion in engagement with a fitting joint projection on the side of the mount base, can be securely welded to the latter by forming a weld over a longer distance along and between marginal edge portions around the notched portion and the fitting joint projection.
Further, according to another preferred form of the present invention, the mount bases are each constituted by a base plate to be fixed on the side of a vehicle body, and a fitting joint projection rising upward from the base plate in such a way as to plug the notched portion.
With the arrangements just described, upon bringing a lower end portion of a pillar into fitting engagement with a fitting joint projection on a mount base, a notched portion in the lower end portion of the pillar is plugged with the fitting joint projection, so that a stronger weld can be formed along marginal edge portions around the notched portion which is in abutting engagement with the fitting joint projection of the mount base.